Sensation Chapter Notes | AP Psychology - Grade 11 PDF Download

Introduction

This chapter explains how we sense the world around us. It covers how our senses detect stimuli like light, sound, and touch, and how our brain processes them. You'll learn about vision, hearing, taste, smell, touch, and balance. These notes are simple and cover everything for the AP Psychology exam.

Overview: Sensation

• Sensation refers to the process by which our sensory organs detect and interpret stimuli from the environment.
• These systems collaborate to capture signals from light, sound, taste, touch, and more, transforming them into neural messages that the brain processes into meaningful perceptions.
• This includes adapting to ongoing stimuli, detecting changes, and, in some cases, experiencing unique sensory overlaps like synesthesia.
• Understanding sensation reveals how we connect with and navigate our surroundings.

Sensation and behavior

Detection of Sensory Information

Sensation starts when environmental stimuli activate sensory organs, converting them into neural signals. For detection to occur, stimuli must surpass specific intensity thresholds.

Key detection concepts:

• Absolute Threshold: The minimum stimulus strength detected 50% of the time.
• Just-Noticeable Difference (JND): The smallest detectable change in stimulus intensity.
• Sensory Adaptation: Reduced sensitivity to prolonged, unchanging stimuli.

Sensory systems often work together through:

• Cross-Modal Processing: Integrating multiple sensory inputs.
• Sensory Interaction: Enhancing overall perception.
• Synesthesia: A condition where one sense triggers another, like seeing colors when hearing sounds.

Change Detection and Adaptation

Our senses are wired to notice changes in stimuli rather than constant inputs, allowing us to focus on significant environmental shifts while ignoring steady backgrounds. 
Weber’s Law explains how we perceive differences:

• JND is proportional to the stimulus’s intensity.
• Stronger stimuli require larger changes to be noticeable.
• Applies to various senses like vision, hearing, and touch.

Adaptation benefits include:

• Filtering out constant noise or stimuli.
• Maintaining sensitivity to new or changing inputs.
• Adjusting to different environmental conditions.
• Optimizing sensory processing for current needs.

Sensory Interaction and Synesthesia

The brain combines inputs from multiple senses to form a unified experience, improving our ability to interpret and respond to the world. 
Common interactions include:

• Taste enhanced by smell and visual cues.
• Speech understanding improved by observing lip movements.
• Balance supported by visual and inner ear signals.

Synesthesia is a unique sensory phenomenon where:

• One sensory input triggers another (e.g., hearing music evokes colors).
• Associations are consistent and involuntary.
• It may enhance memory and creativity.

Visual System and Behavior

Retina and Image Processing

The retina acts as the main visual receptor, transforming light into nerve signals. This intricate tissue is made up of several layers of cells that start analyzing visual information even before it is sent to the brain.
Initial processing includes:

• Detecting light intensity.
• Identifying edges and motion.
• Processing color in cone-rich regions.

The brain compensates for retinal limitations by:

• Filling in the blind spot.
• Ensuring perceptual stability.
• Merging input from both eyes.

Lens Accommodation and Vision

The lens adjusts to focus images on the retina through:

• Changing shape for near or far objects.
• Pupil size changes for light levels.
• Eye muscle coordination for binocular vision.

Vision issues include:

• Myopia: Nearsightedness, images focus before the retina.
• Hyperopia: Farsightedness, images focus behind the retina.
• Astigmatism: Distorted vision due to irregular cornea shape.

Rod Cells and Light Adaptation

Rod cells enable us to see in dim light and play an important role in sensing motion in our side vision. They adjust greatly in response to changing light levels.
Light adaptation occurs when:

• Rod sensitivity decreases in bright light.
• Cones activate for color vision.
• Pupils constrict to limit light.

Dark adaptation is slower, involving:

• Increased rod sensitivity.
• Reduced cone activity.
• Pupil dilation and rhodopsin regeneration.

Theories of Color Vision

Color vision uses multiple processes.

Trichromatic Theory:

• Three cone types: Blue (short-wavelength), green (medium), red (long).
• Each responds to different light wavelengths.
• Combined signals create color perception.

Opponent-Process Theory:

• Colors processed in opposing pairs (red-green, blue-yellow).
• Black-white pair for brightness.
• Explains afterimages and color contrast.

Brain Damage and Vision Disorders

Common disorders:

• Prosopagnosia: Can’t recognize faces.
• Blindsight: Seeing without conscious awareness.
• Visual agnosia: Can’t recognize objects.

Impact depends on:

• Where the damage is.
• How severe the injury is.
• When damage occurred during development.

Auditory System and Behavior

Hearing Anatomy

• Pinna: Outer ear collects sound.
• Tympanic Membrane (eardrum): Vibrates with sound waves.
• Ossicles: Three bones (hammer, anvil, stirrup) amplify vibrations.
• Cochlea: Turns sound waves into neural signals.
• Hair Cells: Convert mechanical energy into neural impulses.

Sound perception and processing

Sound moves as pressure waves with different frequencies and amplitudes. Auditory system turns waves into meaningful sounds.

Sound properties:

• Pitch: Based on wave frequency (measured in Hz).
• Timbre: Based on wave complexity.

Ear processing:

• Outer ear collects sound waves.
• Middle ear amplifies vibrations.
• Inner ear converts vibrations to neural signals.

Theories of pitch perception

Several theories collectively help explain how we perceive pitch at various frequency levels, with each theory focusing on particular elements of how we process sound.

Place theory (high frequencies):

• Different frequencies stimulate different cochlea areas.
• High frequencies affect cochlea base.
• Low frequencies affect cochlea apex.

Frequency theory (low pitches):

• Neurons fire at same rate as sound wave frequency.
• Best for frequencies below 1000 Hz.
• Neural firing matches sound wave patterns.

Volley theory (mid-range frequencies):

• Groups of neurons fire in alternating patterns.
• Handles frequencies up to 4000 Hz.
• Combines place and frequency theories.

Sound localization mechanisms

Locating sound sources uses input from both ears.

Localization depends on:

• Interaural time differences: Sound reaches one ear first.
• Interaural intensity differences: Sound louder in one ear.
• Superior olive: Processes binaural signals.
• Inferior colliculus: Integrates spatial information.
• Auditory cortex: Conscious perception of sound location.

Hearing loss and disorders

Hearing loss can be caused by different factors and may impact various areas of the auditory system. Studying these conditions helps us understand how the hearing system works.

Conduction deafness:

• Issues in outer or middle ear.
• Sound waves don’t reach cochlea properly.
• Often temporary, treatable (e.g., earwax, infections).

Sensorineural deafness:

• Damage to cochlea or auditory nerve.
• Usually permanent.
• Caused by aging, loud noise, or medications.
• Treated with hearing aids or cochlear implants.

Other conditions:

• Tinnitus: Ringing or buzzing sounds.
• Auditory processing disorders: Brain struggles with sound.
• Hyperacusis: Oversensitivity to normal sounds.

Chemical sensory systems and behavior

Olfactory (smell)

Detects airborne chemicals and creates smell perceptions. Only sense that skips thalamus, goes straight to other brain areas.

Olfactory processing:

• Direct connections to limbic system for emotions.
• Bypasses thalamus for faster processing.

Pheromones:

• Chemical signals between same-species members.
• May affect mood, attraction, or body responses.
• Processed by vomeronasal organ in many mammals.
• Possible subtle effects in humans.

Basic taste qualities and perception

Gustation helps evaluate food for nutrition or toxins.

Primary taste qualities:

• Sweet: Sugars, some proteins.
• Sour: Acids.
• Salty: Sodium, minerals.
• Bitter: Potentially toxic compounds.
• Umami: Savory, protein-rich foods.
• Oleogustus: Fatty acids.

Taste sensitivity varies:

• Supertasters: Many taste buds, high sensitivity.
• Medium tasters: Average sensitivity.
• Nontasters: Fewer taste buds, low sensitivity.

Gustatory structures and taste sensitivity

Taste system includes:

• Taste buds with receptor cells.
• Cranial nerves carrying taste signals.
• Thalamus relays to gustatory cortex.
• Orbitofrontal cortex integrates information.

Taste preferences develop from:

• Innate liking for sweet and umami.
• Innate dislike for bitter.
• Culture and personal experiences.
• Conditioning and learning.

Interaction between taste and smell

Flavor comes from combining taste, smell, and other senses.

Taste and smell interact through:

• Retronasal olfaction: Smell during chewing/swallowing.
• Shared pathways in orbitofrontal cortex.
• Complementary sensory information.

Without smell, taste is:

• Limited to basic qualities.
• Less intense.
• Missing flavor complexity.
• Often feels bland or flat.

Other flavor factors:

• Texture (touch input).
• Temperature.
• Visual appearance.
• Sound (e.g., crunchiness).
• Expectations.

Touch Sensory System and Behavior

Somatosensory receptors and processing

Touch provides information about objects and body position.

Mechanoreceptors:

• Merkel cells: Sense pressure and texture.
• Meissner corpuscles: Detect light touch and vibration.
• Pacinian corpuscles: Sense deep pressure and rapid vibration.
• Ruffini endings: Detect skin stretch and joint position.

Neural pathways:

• Sensory neurons to spinal cord.
• Ascending pathways to thalamus.
• Projections to somatosensory cortex.
• Secondary processing in association areas.

Temperature perception mechanisms

Temperature sensation helps maintain body balance and avoid harm.

Thermoreceptors:

• TRPM8: Activated by cold.
• TRPV1: Activated by heat.
• Paradoxical activation: Mixed sensations.

"Hot" sensation from:

• Combined warm and cold receptor activation.
• Central nervous system integration.
• Context based on baseline temperature.
• Pain receptor activation at extreme temperatures.

Vestibular and Kinesthetic Systems and Behavior

Vestibular system tracks head position and movement. Essential for balance and coordinated movements.

Vestibular processing:

• Semicircular canals: Detect rotational movements.
• Otolith organs (utricle, saccule): Sense linear acceleration.
• Hair cells: Convert movement to neural signals.
• Vestibular nuclei: Integrate signals in brainstem.

Balance relies on:

• Vestibular input for head position.
• Visual information about surroundings.
• Proprioceptive feedback from joints/muscles.
• Cerebellum integrating sensory inputs.

Kinesthetic sensing and movement

Kinesthesis: Awareness of body position/movement without vision. Proprioceptive sense enables smooth actions.

Key structures:

• Muscle spindles: Detect muscle stretch.
• Golgi tendon organs: Monitor tension.
• Joint receptors: Sense position.
• Somatosensory cortex: Integrates body position.

Kinesthesis enables:

• Coordinated movements without looking.
• Automatic posture adjustments.
• Spatial awareness of limbs.
• Skilled motor learning through body awareness.